Master Control Station

Located next to the Sector 30 gate at the end of the linac is SLAC’s
newly designated GPS master control station known as SLAC M40. The actual
control point is located on top of a 60 cm diameter concrete pillar with
the top about 3 m off the ground. A wooden deck surrounding the concrete
cylinder provides access. The actual receiver is a Leica System RS 500
Receiver that is housed in a weatherproof box attached to the deck. The
AT-504 choke ring antenna is attached to the top of the pillar using a
Kern forced centering mount. To protect the instruments from lightening, a
lightening arrester is installed at M40.

The official coordinates of the Master Control Station refer to the
Antenna Reference Point (ARP) of the LEICA AT-504 GPS antenna. The ARP is
located at the bottom of the preamplifier as indicated in the antenna
diagram:

The current coordinates are also available in different datum
definitions and with other representations.

Type

Coordinate triplets for SLAC M40 at 2002.90

Datum

XYZ

-2703115.889 m

-4291767.281 m

3854247.836 m

ITRF2000

φ λ
h

37°
24' 59.45851"

-122°
12' 15.34051"

63.689
m

XYZ

-2703115.216 m

-4291768.545 m

3854247.799 m

NAD83

φ λ
h

37°
24' 59.44353"

-122°
12' 15.28996"

64.231
m

NEH

603088.745 m

1849150.025 m

96.743
m

For the datum conversion from ITRF2000 to NAD83 we
used the transformation parameters as published by the National Geodetic Survey (NGS). The
California State Plane coordinates Northing N and Easting E were computed
with NGS's routine spsc83. The orthometric
height H was derived from the ellipsoidal height h by using the GEOID99
geoid undulation value of N=-32.512m.

For the current epoch (2002.90) velocity values have been determined
(using approximately 1.5 years of data). In the ITRF00 and NAD83 reference
frames the velocities take the following values: